well from my knowledge in general, black colors (soil) are HOT in light. i dont grow soil so im not sure about this, just a thought. plus right on the soil like that the humidity will be way higher than just 12" higher, especially if you dont have a lotta airflow. but fo sho everyone must do cuz of differences in everyones setup, is observe, analylize, interpret.... for their own set up. my thermo read 100+ for a week straight in my first grow but had no sign of heat stress. turned out to be the way i had it positioned.